1. Field of the Invention
The current invention is generally related to small motors used for various portable devices and is particularly related to certain parts for holding a shaft with substantially reduced friction in the motors.
2. Description of the Prior Art
A number of small cored motors have been proposed to include rolling bearings and sliding bearings. For example, balls are packed between an outer circle and an inner circle which are fixed in a case or a base/bearing housing. A rotating shaft is supported by these ball bearing units in a cored motor. The size of these ball bearing units increases in proportion to the shaft size not only in the unit width but also in the unit height. The increased unit height is not compatible with dimensional requirements for a thin or flat small motor. The above ball bearing units are also costly for commercial production. To improve these shortcomings of the ball bearing units, a small cored motor includes sintering oil-containing metal as a bearing in the prior art.
Referring to FIG. 1, a cored motor with the sintering oil-containing metal bearing is illustrated in a cross sectional view. A housing unit 1 is a dorm-shaped part and includes a centrally located fixed short cylindrical portion 2 for supporting a shaft 10. The housing unit 1 also includes a ring magnet portion 3, which is located on inside circumference areas of the housing unit 1. A stator base 4 supports a cylindrical bearing housing unit 5, and the cylindrical bearing housing unit 5 holds a first sintering oil-containing metal bearing 6 at a upper portion as well as a second sintering oil-containing metal bearing 7 at a lower portion. A receiving plate 5a is located at the bottom of the bearing housing unit 5 and receives one end of the shaft 10. Stator core 8 is located around an armature coil 9 outside the bearing housing unit 5.
Another prior art cored motor is shown in FIG. 2, another cored motor with the sintering oil-containing metal bearing is illustrated in a cross sectional view. A housing unit 11 is a dorm-shaped part and includes a centrally located fixed short cylindrical portion 16a for supporting a shaft 10. The housing unit 1 also includes a ring magnet portion 13, which is located on inside circumference areas of the housing unit 11. A stator base 14 includes a centrally located fixed short cylindrical portion 17a for supporting a shaft 10. The upper cylindrical bearing housing portion 16a holds a first sintering oil-containing metal bearing 16. The lower cylindrical bearing housing portion 17a holds a second sintering oil-containing metal bearing 17.
In the above described cored motors, friction between the shaft 10 and the sintering oil-containing metal bearings 6, 7 or 16, 17 is substantial at a high rotational speed. As a result of the friction, because the bearings have a relatively short life, the cored motors themselves also have a relatively short life.